Prospective epidemiological studies have shown a strong association between low density lipoprotein-cholesterol (LDL-C) levels and cardiovascular disease (CVD) risk [1]. The subsequent application of statin therapy to decrease these atherogenic LDL-C levels has resulted in a marked reduction of CVD-related morbidity and mortality: every 1 mmol/L decrease in LDL-C results in an estimated 22% reduction of CVD events and a 10% reduction of all-cause mortality [2]. Notwithstanding these impressive benefits, a large residual disease burden persists that has a large impact on both individual patients as well as on global healthcare costs [3]. Novel therapeutics are required to reduce further this residual CVD risk in patients.
One new approach which reduces LDL-C and elevates high-density lipoprotein cholesterol (HDL-C) levels is to inhibit Cholesterol Ester Transfer Protein (CETP). CETP is a plasma protein secreted primarily by liver and adipose tissue. CETP mediates the transfer of cholesteryl esters from HDL to apolipoprotein B (Apo B)-containing particles (mainly LDL and very low density lipoprotein VLDL) in exchange for triglycerides, thereby decreasing the cholesterol content in HDL in favor of that in (V)LDL. Hence, CETP inhibition has been hypothesized to retain cholesteryl esters in HDL-C and decrease the cholesterol content of the atherogenic Apo B fraction.
Despite the evidence supporting the potential of CETP inhibition in reducing cardiovascular morbidity, clinical development of CETP inhibitors has not been straightforward. The first compound to progress to phase III clinical trials was torcetrapib which, although it showed efficacy, was withdrawn from development owing to safety concerns including an unexpected increase in cardiovascular events and death when in combination with atorvastatin, compared with atorvastatin alone [4].
Another CETP inhibitor, dalcetrapib, which entered phase IIb clinical trials was shown to be a weak inhibitor that increased HDL-C by 30-40% with minimal effects on LDL-C concentrations but did not appear to exhibit the off-target effects of torcetrapib [11-13]. Recently, dalcetrapib development has also been terminated on the grounds of futility in a phase III study which was carried out with this compound.
Two more CETP inhibitors, anacetrapib and evacetrapib, are currently in phase III clinical trials. However, a disadvantage of the use of these CETP-inhibitors is that due to the relatively high dosage which has to be used to obtain CETP-inhibition, more and stronger side effects may occur. This can have a negative influence on both the physical well-being of the patient as well as on patient compliance.
Current inventors successfully overcame the above mentioned disadvantages by providing a potent and well tolerated CETP-inhibitor and a pharmaceutical composition thereof. This CETP-inhibitor is the tetrahydroquinoline derivative referred to as Compound A and has the following structural formula:

Clinical studies have shown that Compound A (or a salt thereof) is a potent CETP-inhibitor. Compared to other known CETP-inhibitors, only a relatively low dose of Compound A is needed to reach near complete CETP inhibition. Typically, repeated once daily dosages as low as 2.5 mg of Compound A have proven to be already sufficient to reach near complete CETP-inhibition. These are considerably lower dosages than had to be used for other CETP-inhibitors. Moreover, clinical studies have also shown that Compound A is well tolerated and that it does not lead to serious side effects.
For the preparation of tetrahydroquinoline derivatives, such as Compound A, use has been made of the intermediates according to formula I

Although these kinds of intermediates are very useful in the preparation of tetrahydroquinoline derivatives, such as Compound A, with the current methods for preparing these kinds intermediates, such as described in WO2007/116922, the overall yield is relatively low. Moreover relatively expensive starting materials and catalysts have to be used, such as (R)-3-aminovaleric acid and palladium, respectively. Furthermore, in the current methods of manufacturing problems arise with residual fluorine corroding manufacturing equipment.
Hence, a need exists for an efficient and cost effective process for preparing intermediates according to formula I, which may be used in the further preparation of tetrahydroquinoline derivatives having CETP inhibiting properties, such as Compound A.